The new software does not require the activation code any longer. What you DO need to do is set up an account at TomTom using your email address and provide a p/w.
Log directly into tomtom.com, set up your account, log out.
Now, start up your 720, connect to Home and click on Update My Go. See if that helps.
Also, before doing that, make a complete backup of your unit's contents using Explorer, NOT Home. Ensure hidden folder/files are showing.